There is a problem in pneumatic tires, mostly in heavy-duty pneumatic tires, that uneven wear occurs in a rib portion (a shoulder area) which is on an outer side of the tread in a tire-width direction when a tire is mounted on a steering shaft. The uneven wear in the rib portion includes step wear that causes a step to be formed at a circumferentially-arranged main groove and edge wear that occurs in an outer edge portion due to toe-in, camber, or a slope road surface. Uneven wear in a rib portion may cause a trouble in operation.
In one conventional pneumatic tire, dimensions are set to appropriate values to obtain uneven wear resistance. The pneumatic tire includes a belt layer, and the belt layer includes a first belt on the carcass side and a second belt on the outer side of the first belt. Provided that a tread thickness between the outline of the tread surface and the second belt is T and a tread thickness between the outline of the tread surface and a carcass is K, ratios Tmin/Tc, Tb/Tc, Kmin/Kc, and Kb/Kc are appropriately set: wherein Tmin is a minimum value of the tread thickness T in an area Y that is 0.5 to 0.7 of a half of a ground contact width of the tread, i.e., a width from the tire equator (the distance between the end of a ground contact surface of the tread and the tire equator), Tc is a tread thickness T at the position of the tire equator, Tb is a tread thickness T at the position of the outer edge of the second belt, Kmin is a minimum value of the tread thickness K in the area Y, Kc is a tread thickness K at the position of the tire equator, and Kb is a tread thickness K at the position of the outer edge of the second belt (see, for example, Patent Document 1).
Another conventional pneumatic tire is configured as follows to obtain uneven wear resistance. The pneumatic tire includes one or more belt reinforcing layer that is positioned to the side of an outer circumference of the crown portion of a carcass, a belt that is positioned on an outer side of the belt reinforcing layer in a radial direction of the tire and includes two or more cross belts whose cords cross with each other across the tire equatorial plane, and a tread. The cords of the cross belts are oblique to the tire equatorial plane by 10 to 35 degrees. The belt reinforcing layer is provided in an area having a width narrower than that of the belt in a tire-width-direction cross section and covering a position right under a circumferential direction groove arranged in a shoulder portion (see, for example, Patent Document 2).
Patent Document 1: WO2003/051651
Patent Document 2: Japanese Patent Application Laid-open No. 2004-359030